The present invention relates to a poly(imide-siloxane) compound, more specifically to a poly(imide-siloxane) compound, which can be applied to a passivation layer without an adhesive agent or an adhesive tape for packaging LOC(lead-on-chip) and which has an excellent photoresist wetability and an excellent adhesion with both a silicon chip and a lead frame.
Polyimide(PI) is widely used in semiconductor devices, since it is a polymer material having excellent thermal and mechanical properties such as glass transition temperature and heat resistance. The polyimide to be used for semiconductor buffer coating is applied to the top of a chip before covering an epoxy molding compound(EMC) on the chip. The polyimide applied to the top of the chip serves as a dielectric layer, a passivation layer, an alpha-ray shield layer and the like, and thus protect the chip from contaminants such as exterior moisture and metal ions, and thermal stress.
The recent multifunctional and high capacity trend in semiconductor chips has brought changes in chip packages, one of which is the lead-on-chip (LOC) structure. In this structure, a die pad-free lead frame and the chip are fixed with a double-coated adhesive tape. Accordingly, as the area of the silicon chip is larger than that of the conventional one even with same outer area as the conventional one, a chip package having high capacity can be produced. Further, as the length of wiring bonding is shortened and the transmission of the signal becomes fast, the heat generated by the consumption of high electric power is emitted, and the size of the device is reduced.
In the structure of the LOC-type package, the versatile adhesive interfaces between chip and polyimide, polyimide and EMC, polyimide and lead frame, lead frame and EMC and the like are formed, and the strong adhesive strength in these interfaces should be retained even in severe conditions such as high temperature and high humidity, in order to attain a reliable semiconductor chip.
In the past, silane coupling agents or siloxane-modified polyimides containing a 1,3-bis(3-aminopropyl)tetramethyldisiloxane were used for adhering the silicon chip with the polyimide passivation layer, and an adhesive tape was used for adhering a polyimide passivation layer with a lead frame. Examples of the adhesives include an adhesive having a high melting point consisting of a polyamide-imide or a polyamide disclosed in unexamined Japanese patent publication No. 282,283; a polyimide adhesive disclosed in unexamined Japanese patent publication No. 157,190; and a thermosetting polyimide adhesive film disclosed in unexamined Japanese patent publication Nos. 235,382; 235,383; and 15,663.
However, since the foregoing polyamide-imide or polyamide adhesive film have high water absorption due to hydrophilic amide group contained therein, the reliability is low when it is used as an electronic material. Polyimide cannot be used in electronic parts sensitive to heat, pressure, water, etc., because it has to be semi-cured at a high temperature of 275xc2x0 C. and a high pressure of 50 kgf/cm2 for a long time of 30 minutes in an adhering process. Furthermore, it produces water during the course of the curing process. U.S. Pat. No. 5,739,263 discloses the use of an adhesive tape introducing a siloxane to a polyimide. But, in the case of a long chain of siloxane modified polyimide, the tape is too opaque to be directly used as a passivation layer as well as to be applied to the process for manufacturing a semiconductor. Moreover, the photoresist cannot be coated, since the surface is too non-polar. U.S. Pat. Nos. 5,942,592; 5,739,263; and 4,389,504 disclose that since the polyimide is modified with a siloxane, i.e. polydimethyl siloxane having only one kind of molecular weight, it cannot have excellent thermal and mechanical properties.
Alternatively, a siloxane is introduced to increase adhesive strength. As the molecular weight of the siloxane is increased, the adhesive strength with the lead frame is also increased, but the adhesive strength with the silicon chip is reduced. In this case, an adequate distribution of the molecular weight having a high adhesive strength with both the silicon chip and the lead frame has to be determined.
Moreover, the more the molecular weight and the siloxane content are increased, the more the film is opaque due to phase-separation, and the more the surface of the film becomes non-polar, thus deteriorating the wetability of the photoresist. Accordingly, the lithography process cannot be carried out.
As a result of the present inventors"" earnest studies for solving the above problems, they have found that a poly(imide-siloxane) compound for packaging LOC having excellent thermal and mechanical properties, and low moisture absorption, which can be applied to a LCC package without an adhesive or an adhesive tape, has an excellent adhesive strength with both silicon chip and lead frame, and has an excellent wetability of the photoresist.
A feature of the present invention is to provide a poly(imide-siloxane) compound for packaging LOC having a high adhesive strength with both silicon chip and lead frame by defining the distribution of the molecular weight of the siloxane.
Another feature of the present invention is to provide a poly(imide-siloxane) compound for packaging LOC, which has an excellent wetability of the photoresist and is capable of carrying out a lithography process by controlling the domain size of the phase-separated siloxane and changing the chemical structure of the siloxane.
Still another feature of the present invention is to provide a poly(imide-siloxane)compound for packaging LOC, which can be used as a passivation layer without silane coupling agents or adhesive tapes.
Still another feature of the present invention is to provide a poly(imide-siloxane)compound for packaging LOC, which is capable of reducing the cost for manufacturing the semiconductor by saving the cost of material and shortening the processes due to no additional use of coupling agents or adhesive tapes.
In accordance with one aspect of the present invention, there is provided a poly(imide-siloxane) compound for packaging LOC which is produced by reacting, in a polar solvent, a diaminosiloxane compound of the formula(1) 
wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are independently an aromatic group, aliphatic group or halogenated hydrocarbon, hydroxy, or ether group, and the sum xe2x80x9cm+nxe2x80x9d is an integer of 0 to about 1000 (0xcx9c1000); and a diamine compound of the formula(2)
H2Nxe2x80x94Rxe2x80x94NH2 xe2x80x83xe2x80x83(2) 
wherein R is one of the following groups: 
with an aromatic tetracarboxylic dianhydride of the following formula (3), with the number of moles of compound (3) being the same as the total number of moles of the compounds (1) and (2) 
wherein A is one of the following groups: 
In accordance with another aspect of the present invention, there is provided a composition including a mixture of at least two compounds as described above. In a first compound of the mixture, m+n is 14 or less, while in a second compound of the mixture, m+n is 14 or more.
According to a further aspect of the present invention, an electronic device is provided that includes a silicon chip, a lead frame and a passivation layer that includes a compound as described above. The compound adheres to both the silicon chip and the lead frame without the need for an additional adhesive.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.